Liquid crystal display device and method for fabricating the same

ABSTRACT

A liquid crystal display (LCD) device includes a first substrate and a second substrate, an organic light emitting element formed by interposing a first insulating layer on an outer surface of the first substrate, a second insulating layer and a protective layer formed in order over an entire surface of the organic light emitting element, a thin film transistor formed on the first substrate, a passivation layer formed over an entire surface of the first substrate including the thin film transistor, a pixel electrode formed on the passivation layer to be connected to the thin film transistor, a common electrode formed on the second substrate, and a liquid crystal layer formed between the first substrate and the second substrate. A method for fabricating the LCD includes the steps of forming a first insulating layer on an outer surface of a first substrate, forming an organic light emitting element on the first insulating layer, forming a second insulating layer over an entire surface of the organic light emitting element, forming a protective layer on the second insulating layer, forming a thin film transistor on the first substrate, forming a passivation layer over an entire surface of the first substrate including the thin film transistor, forming a pixel electrode on the passivation layer, and forming a liquid crystal layer between the first substrate and a second substrate.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.2000-86010 filed on Dec. 29, 2000, the entirety of which is herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device, and in particular, toa liquid crystal display (LCD) device.

2. Description of the Related Art

An LCD is not a self-emissive light element but instead is a lightreceiving element necessitating an independent light source, and has atechnical limitation in terms of brightness, contrast, angle of visualfield, magnification of the view, etc. Therefore, efforts have beenactively made to develop a novel flat display device. An example isresearch into an organic electroluminescent (EL) device that has meritssuch as operability with low voltage, self-emission of light, a compactand slim appearance, wide angle of visual field and a quick response.

The EL of an organic material was first discovered in single crystalAnthracene. Nevertheless, the first discovery failed to develop the ELdevice for more than the next 20 years due to its size limit anddifficulty in growing the single crystal, as well as to an extremelyhigh voltage (˜1000V) required for its operation. Recently, however, adevice has been developed having a film thickness of only 1000 Å andoperable with a low voltage of about 10V.

An organic light emitting diode (OLED) comprises a cathode layer, anorganic film layer, and an anode layer. The organic film layer comprisesan electron transport layer, a hole transport layer, and an organicemitting layer. If necessary, an electron injection layer and a holeinjection layer may be additionally comprised of the organic film layer.

An inorganic EL device is similar to a compound in its concept that afluorescent material is emitted by electric energy. However, a slightdifference lies in terms of the excitation, which is a core of theemitting mechanism. In the inorganic EL device, light emission is causedby energy generated by an acceleration and collision of electrons due tohigh voltage. In the organic EL device, however, light emission iscaused by rebinding of the holes injected from an anode and a cathodewith electrons.

The following is a detailed description of a conventional LCD made withreference to FIG. 1.

FIG. 1 is a sectional view of a conventional LCD illustrating astructure thereof.

Referring to FIG. 1, the conventional LCD comprises two insulatingsubstrates 101, 101 a facing each other and having liquid crystal sealedtherebetween, color filter layers 102 of red, green and blue formed onthe upper substrate 101 for expressing colors, and black matrices 103for shielding penetration of light into the parts other than the pixelelectrodes formed on the lower substrate 101 a.

A common electrode 105 is formed to cover the color filter layers 102and the black matrices. It is possible to form an overcoat 104 beforeforming the common electrode 105.

Thin film transistors consisting of a gate electrode 106 elongated froma gate line, a source electrode 107 and a drain electrode 108 elongatedfrom a data line, which is arrayed to cross the gate line, are formed onthe lower substrate 101 a at regular intervals. A pixel electrode isconnected to the drain electrode 108 through a contact hole. A backlight112 is provided on an outer surface of the lower substrate 101 a.

Spacers 109 are dispersed between the color filter layers and thin filmtransistors to maintain a cell gap.

However, the conventional LCD and its fabrication method pose thefollowing problems.

An LCD is not a self-emissive light element but a light receivingelement necessitating an independent light source, thereby requiring abacklight. The electric power consumed by the backlight occupies adominant part of the electric power supplied to the LCD. Further, thebacklight becomes a bar to reducing weight, thickness, length and sizeof the LCD.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide an LCDand a method for fabricating the same that can overcome the easybreakability of the conventional LCD by employing an organic lightemitting diode as a backlight of the LCD to reduce the thicknessthereof, and by using an organic material like polymer.

To achieve the above object, there is provided an LCD comprising: afirst substrate and a second substrate; a light emitting layer formed onan outer surface of the first substrate; a thin film transistor and apixel electrode formed on the first substrate; a common electrode formedon the second substrate; and a liquid crystal layer formed between thefirst substrate and the second substrate.

There is also provided a method for fabricating an LCD, comprising thesteps of: preparing a first substrate and a second substrate; forming alight emitting layer on an outer surface of the first substrate; forminga thin film transistor and a pixel electrode formed on the firstsubstrate; and a liquid crystal layer between the first substrate andthe second substrate.

The light emitting layer comprises a first insulating layer, an organiclight element, and a second insulating layer. The organic light elementcomprises a first electrode, a hole transport layer, an organic lightemitting layer, electron transport layer, and a second electrode.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

The advantageous effects of the present invention include overcoming theeasy breakability of the conventional LCD by employing an organic lightemitting diode as a backlight of the LCD to reduce the thicknessthereof, and by using an organic light element as a substitute for abacklight, thereby reducing weight, thickness, length and size of theLCD and enhancing efficiency of electric power.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a sectional view of a conventional LCD illustrating astructure thereof;

FIG. 2 is a sectional view of an LCD according to a preferred embodimentof the present invention illustrating a structure thereof; and

FIGS. 3A to 3D are views of an LCD according to a preferred embodimentof the present invention illustrating a method for fabricating the same.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described hereinbelow with reference to the accompanying drawings. In the followingdescription, well-known functions or constructions are not described indetail since they would obscure the invention in unnecessary detail.

FIG. 2 is a sectional view of an LCD according to a preferred embodimentillustrating a structure thereof.

Referring to FIG. 2, the LCD comprises two insulating substrates 201 a,201 b facing each other having liquid crystal 211 sealed therebetween. Afirst insulating layer 202 is formed on an outer surface of theinsulating substrate 201 a. An anode 203 of indium tin oxide (ITO)material is formed on the first insulating layer 202. An organic filmlayer 204 is formed on the anode 203. The organic film layer 204comprises a hole transport layer(204 a), an organic light emittinglayer(204 b), and an electron transport layer(204 c). A cathode 205 ofMg or Li material is formed on the organic film layer. A secondinsulating layer 206 is formed on the cathode 205, and a protectivelayer 207 is formed on the second insulating layer 206.

Here, the first substrate 201 a is of polymer such as polycarbonate(PC), polyimide, polyethersulphone (PES), polyacrylate (PAR),polyethylenenaphthelate (PEN), or polyethyleneterephehalate (PET) havingflexibility that can avoid easy breakability of the conventional glasssubstrate. The first substrate 201 a and the second substrate 201 bperform an additional function of polarization deriving from themolecular array of a macromolecular organic material.

Sheet glass of a predetermined thickness is formed on an outer surfaceof the first substrate 201 a before the first insulating layer 202 isformed so as to shape the polymer substrate.

Meanwhile, a thin film transistor 208 comprising a gate electrode, agate insulating film, a semiconductor layer, a source electrode, and adrain electrode is formed on an upper portion of the first substrate 201a by undergoing a series of processes. A passivation layer 209 islaminated over the entire surface including the thin film transistor208. Pixel electrodes 210 are formed on the passivation layer 209 atpredetermined intervals.

A common electrode 212 is formed on the second substrate 201 b. Colorfilter(213) layers as well as black matrices(214) may be additionallycomprised to express colors and to shield penetration of light into thethin film transistor 208 of the first substrate 201 a, respectively.

FIGS. 3A to 3D are views of an LCD according to the preferred embodimentillustrating a method for fabricating the same.

As shown in FIG. 3A, the first insulating layer 202, preferably composedof SiO₂ or SiNx, is formed on an outer surface of the first substrate201 a.

As shown in FIG. 3B, an ITO film is deposited on the first insulatinglayer 202 by means of sputtering to form the anode 203. Thereafter, theorganic film layer 204 is formed on the anode 203 by forming a holetransport layer(204 a), an organic light emitting layer(204 b) and anelectron transport layer(204 c) successively by means of vacuumdeposition or spin coating of an organic material such as Alq3(tris-8-hydroxyquinolinato aluminum), BeBq(bis-benzo-quinolinato-berellium), PPV (polyphenylenevinylene) orpolyalkylthiphene. The organic material should satisfy the followingcharacteristics: a high fluorescent quantum yield under solid state; ahigh mobility of electrons and holes; and uneasy decomposability duringvacuum deposition; an evenly formed film; and a film with a stablestructure.

The cathode 205 is formed on the organic film layer 204 by depositing aconductive material, preferably a metallic material such as Mg, Li or acompound of Mg and Li, by means of sputtering.

As shown in FIG. 3C, the second insulating layer 206 is formed on thecathode 205, and the protective layer 207 is subsequently formed thereonto prevent deterioration of the cathode 205 caused by moisture andoxygen. The protective layer is preferably composed of SiO_(x) orIO_(x).

As shown in FIG. 3D, the thin film transistor (TFT) 208 comprising agate electrode, a gate insulating film, a semiconductor layer, a sourceelectrode, and a drain electrode is formed on the first substrate byundergoing a series of processes. The passivation layer 209 is laminatedover the entire surface including the thin film transistor 208.Thereafter, pixel electrodes 210 are formed on the passivation layer 209at predetermined intervals.

Though not shown in the drawing, the fabrication of the LCD is completedby disposing the first substrate 201 a, on which the organic lightemitting diode has been formed, and the second substrate 201 b as wellas by injecting liquid crystal therebetween.

Meanwhile, the method for fabricating the LCD according to the preferredembodiment may comprise the steps of forming an active region on thefirst substrate, and forming the organic light emitting diode on anouter surface of the first substrate. The method may further comprisethe steps of disposing the first substrate and the second substrate, andforming the organic light emitting diode.

As described above, an LCD and a method for fabricating the same asdisclosed herein have the following advantageous effects.

The LCD as disclosed herein is much slimmer than the conventional LCDowing to an employment of an organic light emitting diode as abacklight. Also, the LCD as disclosed herein is not liable to be brokenowing to an employment of an organic material for the substrates.Further, the polarizing function in the substrates of the LCD asdisclosed herein does not necessitate any polarized plate, therebyserving to simplify the fabricating process.

While the invention has been shown and described with reference to acertain preferred embodiment thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1-37. (canceled)
 38. A method for fabricating a liquid crystal display(LCD) device, comprising: depositing a first insulating layer on a firstsurface of a first substrate; after depositing the first insulatinglayer, sequentially depositing a first electrode on the first insulatinglayer, an organic film layer on the first electrode and a secondelectrode on the organic film layer to form a light emitting structure;after forming the light emitting structure, depositing a protectivelayer to protect the light emitting structure; forming a thin filmtransistor array on a second surface of the first substrate; providing aliquid crystal layer on the second surface of the first substrate; andattaching the first substrate to a second substrate.
 39. The method ofclaim 38, wherein the light emitting structure is a light emittingdiode.
 40. The method of claim 38, wherein forming the organic filmlayer comprises: forming a hole transport layer; forming an organiclight emitting layer; and forming an electron transport layer.
 41. Themethod of claim 40, wherein the organic light emitting layer comprisesany one of Alq3 (tris-8-hydroxyquinolinato aluminum), BeBq(bis-benzo-quinolinato-berellium), PPV (polyphenylenevinylene) orpolyalkylthiphene.
 42. The method of claim 38, wherein the firstelectrode is indium tin oxide.
 43. The method of claim 38, wherein thefirst substrate is comprised of an organic material.
 44. The method ofclaim 43, wherein the first substrate performs an additional function ofpolarization.
 45. The method of claim 38, wherein the first insulatinglayer includes either SiOx or SiNx.
 46. The method of claim 38, whereinthe protective layer includes SiOx or IOx.